1. Field of the Invention
The present invention relates generally to the melt spinning of polycaprolactam. In particular, it relates to a continuous process for producing a staple fiber product by the direct spinning of polycaprolactam from an equilibrium melt.
2. Prior Art Statement
In the commercial evolution of processes for the melt spinning of polycaprolactam, it has been recognized for some time that the direct utilization of an equilibrium melt from a standard polymerization of caprolactam could afford economic advantages over commonly-employed processes utilizing polymer chips from which monomeric and oligomeric materials have been removed. Indeed, a number of "direct spinning" processes have been proposed over the years, in an effort to attain the economy of operation which is so desirable. However, all of these expedients have been found wanting, in that none actually affords the desired economy of operation in combination with the process efficiency and efficacy necessary to produce the quality product which is required in the marketplace. The closest prior art is considered to be:
1. U.S. Pat. No. 2,733,122 (Herele, et al). This patent discloses a process for producing staple fibers from epsilon-aminocaproic acid condensation products which contain water-soluble monomeric and oligomeric materials. The process is the sequential combination of the following procedural steps: (a) extruding filaments of the aforementioned epsilon-aminocaproic acid condensation products and combining these filaments into a tow of at least 40,000 denier; (b) placing a tension upon the tow to stretch the filaments to a multiple of their length; (c) washing the stretched tow with a hot aqueous washing agent; (d) drying the washed tow to a degree of moisture of less than 6 percent; the washing and drying of the tow being accomplished while tension is being maintained on the tow; (e) crimping the dried filaments of the tow in a continuous mechanical crimper while maintaining the moisture content of less than 6 percent; followed by cutting the crimped tow into staple fibers and opening the staple fibers by means of an air jet. Nowhere comprehended in this reference are the following essential limiations found in the present process: (a) the employment of a two-phase quenching technique to lower the temperature of the extruded filaments to a value between about 30.degree. and 70.degree. C. before drawing thereof is effected; (b) drawing, crimping, and cutting the unextracted filamentary polymeric material, to the surface of which a drawing and crimping lubricant and antistatic agent has been applied; and (c) the employment of a particularly-defined asymmetric spinnerette as a preferred embodiment. PA1 2. U.S. Pat. No. 2,703,433 (Holzmann). This patent discloses a spinnerette for the production of filaments used in making staple fibers. Provided is a plate having a plurality of spinning orifices arranged in groups spaced from each other to provide concentric annular opening--free channels in the plate and radial opening--free channels in the plate extending toward the center. The spacing between the groups of spinning openings providing the radial and annular opening--free channels is substantially greater than the spacing between the individual spinning openings in each group, which are arranged in a plurality of rows disposed at different distances from the center of the plate. Although an asymmetric arrangement of spinning orifices is presented, there is no disclosure or suggestion of the configuration considered especially preferred in the practice of the present invention, viz., the space between adjacent spinning orifices increases from each side of the spinnerette to the center thereof and from the front to the back thereof. PA1 3. U.S. Pat. No. 3,047,541 (K. Ryffel, et al). This patent discloses a process for the continuous production of polyamide fibers by the direct spinning of a polycaprolactam melt containing monomeric and oligomeric material. The extrudate is immediately stretched to produce fibers having a very low elongation at break. Stretching is facilitated by treating the surface of the extrudate with an emulsifying oil. Nowhere disclosed or suggested are the following essential limitations found in the present process: (a) the employment of a two-phase quenching technique to lower the temperature of the extruded filaments to a value between about 30.degree. and 70.degree. C. before drawing thereof is effected; (b) crimping and cutting the unextracted filamentary polymeric material after drawing thereof, and after a drawing and crimping lubricant and antistatic agent (preferably water) has been applied; and (c) the employment of a particularly-defined asymmetric spinnerette as a preferred embodiment. PA1 A. Spinning an equilibrium melt from a standard hydrolytic or anionic polymerization of caprolactam, the equilibrium melt containing methanol-extractable material including monomeric and oligomeric substances, the equilibrium melt being spun at a temperature of between about 230.degree. and 270.degree. C. through a spinnerette, the spinning take-away speed being less than about 250 meters/minute; PA1 B. Quenching the molten polycaprolactam in two phases: PA1 C. Applying a drawing and crimping lubricant and antistatic agent to the surface of the filamentary polycaprolactam; PA1 D. Drawing the filamentary polycaprolactam by conventional means at a total draw ratio between about 3 and 5; PA1 E. Crimping the drawn filamentary polycaprolactam by essentially conventional means; PA1 F. Cutting the crimped filamentary polycaprolactam into staple lengths by conventional means; PA1 G. Subjecting the filamentary polycaprolactam staple to a multiple stage washing procedure for removal of extractables; PA1 H. Drying the washed filamentary polycaprolactam staple by conventional means; and PA1 I. Packaging the dried filamentary polycaprolactam staple for subsequent use or sale.
In fact, the prior art, as particularized by the references set forth above, actually presents a background against which the present invention stands out as a valuable improvement. This will become apparent to those of skill in the art upon a study of the present invention as specified hereinafter.